snappyHexMesh bumps (bulges) when using different refinementSurfaces levels

Summary

When using different refinementSurfaces levels, for example 5 6, mesh gets bumps (bulges) and while possible to get rid of them by changing minTetQuality to -1e+30 that change makes CFD very unstable and in most cases results in a crash.

• Bumps mainly appear when reducing skewness from 20 4 to 4 2 and lower. Leaving skewness high again comes at the cost of stability during the run.
• Bumps often occur at the transition from one refinement level to another
• The bumps go away when using the same refinement level everywhere on the surface but that eliminates the possibility for local refinement

Steps to reproduce

Run attached case and open Paraview, and you'll see bumps the top of the wind shield.

Example case

See attached

What is the current bug behaviour?

Bumps appear at the transition from one refinement level to another

What is the expected correct behaviour?

Bumps should not be appearing on the surface when using different refinement levels

Relevant logs and/or images

This image shows bumps for maxBoundarySkewness 20 maxInternalSkewness 4 which is default value

Using maxBoundarySkewness 2 maxInternalSkewness 2 bumps are even more pronounced

Environment information

• Operating system : Ubuntu 20.04
• OpenFOAM version : 2012
• Hardware info : AMD EPYC 7401P 24-Core Processor
• Compiler : GCC

Possible fixes

• Increase skewness (to the default values of 20 4) (but reduces solver stability)
• set minTetquality to -1e+30 (but reduces solver stability significantly)

bumps.zip